* Scottish Gaelic (Gàidhlig): While there's a push towards standardization, significant dialectal differences exist across Scotland. A speaker of, say, Lewis Gaelic might struggle with someone from the Southern Hebrides, even if both are speaking Scottish Gaelic.
* Irish Gaelic (Gaeilge): Similar to Scottish Gaelic, Irish Gaelic has many dialects, with varying degrees of mutual intelligibility. A speaker from County Donegal might not fully understand someone from County Kerry.
* Manx Gaelic (Gaelg): This is a separate language, largely extinct until a revival effort, and it is significantly less mutually intelligible with Scottish or Irish Gaelic.
While speakers of different Gaelic languages might share some vocabulary and grammatical structures, the differences are substantial enough that mutual intelligibility isn't guaranteed. Someone speaking "standard" Scottish Gaelic wouldn't be automatically understood by an Irish Gaelic speaker, and vice-versa. Manx Gaelic would be even more challenging.